Placenta previa (pluh-SEN-tuh PREH-vee-uh) occurs when a baby's placenta partially or totally covers the opening in the mother's cervix — the lower end of the uterus that connects to the top of the vagina. Placenta previa can cause severe bleeding before or during delivery.

The placenta provides oxygen and nutrients to your growing baby and removes waste products from your baby's blood. It attaches to the wall of your uterus, and your baby's umbilical cord arises from it. In most pregnancies, the placenta attaches at the top or side of the uterus. In placenta previa, the placenta attaches to the lower area of the uterus.

If you have placenta previa, you'll probably be restricted from physical exertion for a portion of your pregnancy and you'll likely require a cesarean section (C-section) to safely deliver your baby.

Bright red vaginal bleeding without pain during the second half of pregnancy is the main sign of placenta previa. Bleeding ranges from light to heavy. The bleeding usually stops without treatment, but it nearly always returns days or weeks later. Some women also experience contractions.

When to see a doctor

If you have vaginal bleeding during your second or third trimester, call your doctor right away. If the bleeding is severe, seek emergency medical care.

The placenta grows wherever the embryo implants itself in the uterus. If the embryo implants itself in the lower portion of the uterus, the placenta might grow over the cervix — causing placenta previa.

Most cases of placenta previa are diagnosed during a second trimester ultrasound examination. If the placenta just barely reaches the cervix, expansion of the uterus may pull the placental attachment higher, away from the cervix, which will resolve the situation.

If the placenta is across the cervix, however, it's unlikely to resolve with time. The later in pregnancy that placenta previa exists, the more likely it will be present at the time of delivery.

Persistent types of placenta previa have been associated with:

Scars in the lining of the uterus, such as from previous surgery

A large placenta, such as with a multiple pregnancy

Being 35 or older during pregnancy

Having had babies

Women are at higher risk for placenta previa if they've had previous surgeries involving the uterus, such as:

A C-section

Surgery to remove uterine fibroids

Dilation and curettage, though this presents a much lower risk

Placenta previa is also more common among women who:

Have delivered at least one baby

Had placenta previa with a previous pregnancy

Are carrying more than one fetus

Are age 35 or older

Are of a race other than white

Smoke

Use cocaine

If you have placenta previa, your health care provider will monitor you and your baby to reduce the risk of these serious complications:

Bleeding. Severe, possibly life-threatening vaginal bleeding (hemorrhage) can occur during labor, delivery or the first few hours after delivery.

Preterm birth. Severe bleeding may prompt an emergency C-section before your baby is full term.

If you've been pregnant for more than 12 weeks and you develop vaginal bleeding, call your pregnancy health care provider. He or she may recommend immediate medical care depending on your symptoms, your personal health history and how far along you are in the pregnancy.

What you can do

Before your appointment, you may want to:

Ask about pre-appointment restrictions. In most cases, you'll be seen immediately. However, if your appointment will be delayed for a day or two, ask whether you should restrict your activity in the meantime.

Arrange to bring a family member or friend. The fear you may have about bleeding during pregnancy can make it difficult to focus on what your health care provider says. Take someone along who can help you gather the information.

Write down your questions. Having a list of questions can help you make the most of your time with your health care provider.

Below are some basic questions to ask your health care provider about placenta previa. Don't hesitate to ask any other questions.

Do I have placenta previa?

Is there a chance it could resolve on its own?

What treatment do you recommend?

What follow-up care will I need during the rest of my pregnancy?

Is there anything I can do to help bring my pregnancy to term?

What restrictions do I need to place on activity? For how long?

What signs or symptoms, if they occur, should cause me to call you?

What signs or symptoms, if they occur, should cause me to go to the hospital?

Will I be able to deliver vaginally?

Does this condition increase the risk of complications during future pregnancies?

What to expect from your doctor

Your health care provider is likely to ask you a number of questions, including:

When did you first notice vaginal bleeding?

Did you bleed only once, or has the bleeding come and gone?

How heavy is the bleeding?

Is the bleeding accompanied by pain or contractions?

Have you had previous pregnancies I'm not aware of?

Have you had uterine surgeries, including C-section, fibroid removal, or dilation and curettage after a miscarriage or abortion?

Do you or did you smoke? How much?

How far do you live from the hospital?

How long would it take to get to the hospital in an emergency, including time to arrange child care and transportation?

Do you have someone nearby who could care for you if you need bed rest?

Placenta previa is diagnosed through ultrasound, either during a routine prenatal appointment or after an episode of vaginal bleeding.

A definitive diagnosis may require a combination of abdominal ultrasound and transvaginal ultrasound, which is done with a wand-like device placed inside your vagina. Your health care provider will take care with the position of the transducer in your vagina so as not to disrupt the placenta or cause bleeding. In rare instances, magnetic resonance imaging (MRI) may be used to clearly determine placental location.

If your health care provider suspects placenta previa, he or she will avoid routine vaginal exams to reduce the risk of heavy bleeding. You may need additional ultrasounds to check the exact location of your placenta before delivery. Your baby's heartbeat may be tracked as well.

Treatment for placenta previa depends on various factors, including:

The amount of bleeding

Whether the bleeding has stopped

How far along your pregnancy is

Your health

Your baby's health

The position of the placenta and the baby

For little or no bleeding

If you have little or no bleeding, your health care provider may recommend bed rest at home. In some cases, you may need to lie in bed most of the time — sitting and standing only when necessary.

You'll need to avoid sex, which can trigger bleeding. Exercise is usually off-limits, too. Be prepared to seek emergency medical care if you begin to bleed. You'll need to be able to get to the hospital quickly if bleeding resumes or gets heavier.

If the placenta doesn't completely cover your cervix, you may be allowed to attempt a vaginal delivery. If you begin to bleed heavily, you may need an emergency C-section.

For heavy bleeding

If you're bleeding, you may need hospital bed rest. Severe bleeding may require a blood transfusion to replace lost blood. You may also benefit from medications to prevent premature labor.

Your health care provider will likely plan a C-section as soon as the baby can be delivered safely, ideally after 36 weeks of pregnancy. If you need a C-section before 36 weeks, you may be given corticosteroids to speed your baby's lung development.

For bleeding that won't stop

If your bleeding can't be controlled or your baby is in distress, you may need an emergency C-section — even if the baby is premature.

Pregnancy is supposed to be a time of happy anticipation. If you're diagnosed with placenta previa, you're sure to worry about how your condition will affect you, your baby and your family. Some of these strategies may help:

Learn about placenta previa. Gathering information about your condition may help you feel less scared. Talk to your health care provider, do some research on your own and connect with other women who've had placenta previa.

Prepare for a C-section. Placenta previa may prevent you from delivering your baby vaginally. If you're disappointed that you may not have a vaginal birth, remind yourself that your baby's health and your health are more important than the method of delivery.

Make the best of bed rest. Fill your days by planning for your baby's arrival. Read about newborn care or purchase newborn necessities, either online or by phone. Or use the time to balance your checkbook, organize old photo albums or catch up on thank-you notes.

Take care of yourself. Surround yourself with things that comfort you, such as a good book or music you love. Give your partner, friends and loved ones concrete suggestions for ways to help, such as bringing a favorite food or simply stopping by for a visit.

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